The present invention relates generally to the preparation of fluorinated organic compounds. More specifically, the invention relates to the preparation of fluorinated organic compounds by a liquid-phase, catalytic fluorination process.
The production of fluorinated organic compounds, such as hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), is well known in the art. Among the more popular fluorination methods is liquid-phase, catalytic fluorination which is of particular interest herein. In this type of fluorination, a liquid starting material is reacted with a fluorination agent in a reactor in the presence of a liquid catalyst and under conditions sufficient to form a fluorinated organic compound. The fluorinated organic compound readily vaporizes under the reaction conditions and leaves the reactor as a vapor in a product stream. The product stream then is distilled to recover the fluorinated organic compound.
Although widely used, conventional liquid-phase fluorination suffers from several shortcomings. One of the more significant shortcomings is the formation of high-boiling by-products. As used herein, xe2x80x9cby-productxe2x80x9d refers to any compound that is produced in the fluorination process and that is neither the desired HFC/HCFC, nor a fluorinated intermediate. The most common by-products are chlorinated by-products. Chlorinated by-products are formed at particularly high levels when chlorine is added to the reaction to regenerate the catalyst. For example, in the production of 1,1,1-trifluoroethane (HFC-143a), the use of chlorine increases substantially the formation of the by-product 1,2-dichloro-1,1-difluoroethane (HCFC-132b). Chlorinated by-products can be formed also in side reactions with the fluorination catalyst.
Chlorinated by-products tend to have higher boiling points than those of the fluorinated product; consequently, they tend not to vaporize during fluorination. Over time, the chlorinated by-products accumulate in the reactor necessitating periodic shut-downs to boil off or drain them from the reactor. Shutting down the reactor disrupts the continuous fluorination process and thereby reduces production efficiency. Additionally, once accumulation of by-products begins, the space available for fluorination decreases, thereby further reducing production efficiency. Therefore, a need exists for a more efficient approach to preparing HFCs and HCFCs, including an approach that avoids the accumulation of high-boiling by-products in the reactor. The present invention fulfills this need among others.